Method of spinning solutions of polyacrylonitrile or mixed polymers thereof



Jan. 29, 1957 E. HEISENBERG ETAL 2,779,746

METHOD OF SPINNING SOLUTIONS OF POLYACRYLONITRILE OR MIXED POLYMERS THEREOF Filed Nov. 14, 1952 ATTORNEY United States Patent METHOD OF SPINNING SOLUTIONS OF POLYACRYLONITRILE OR MIXED POLY- MERS THEREOF Erwin Heisenberg and Ernst Pirot, Erlenbach (Main), Germany, assignors to Vereinigte Glanzstoff Fabriken Aktiengesellschaft, WuppertaleElberfeld, Germany, a joint-stock company of Germany Application November 14, 1952, Seriai No. 320,370

Claims priority, application Germany November 17, 1951 7 Claims. (Cl. 26032.6)

This invention relates to spinning methods, and more particularly to processes of spinning solutions of polyacrylonitrile or mixed polymers thereof.

It is well known in the art that dissolution of polyacrylonitrile or mixed polymers thereof, in such solvents as were heretofore considered conventional, e. g. dimethyl formamide, butyrolactone, formyl pyrrolidine, etc., frequently led to inhomogeneous solutions. In the course of the subsequent spinning step such solutions prove troublesome in that they cause breakage of threads, variations of denier etc. Moreover, these solutions as well as the threads deriving therefrom, exhibit a light yellow coloration.

It is a principal object of this invention to eliminate these drawbacks.

Other objects, and the manner in which the same are attained, will become apparent as this specification proceeds.

We have discovered that polyacrylonitrile solutions can be spun with excellent results and without any difficulty if the solution is prepared in the manner explained hereinafter and is spun immediately thereafter. According to this invention a homogeneous solution of acrylonitrile is obtained by converting a finely ground polyacrylonitrile having a particle size below 10011., by agitation in dimethyl formamide or some other suitable solvent, into a dispersion. Another significant step involves evacuation while the dispersion is being formed. To this end, the finely ground polyacrylonitrile is passed, under thorough agitation and in a uniform manner, into an evacuated vessel filled with dimethyl formamide or some other suitable solvent and, the vacuum is maintained .during the formation of the dispersion. The preparation of a finely divided dispersion which, is freed from air signifies a particularly important advantage over the spinning processes of the prior art. The invention contemplates further keeping, during formation of the dispersion, the temperature as low as possible while, at the same time, providing a high vacuum. Temperatures between and 30 C. are contemplated by the invention, the preferred temperature range extends from 0 to about 15 C. The vacuum is so selected that the solvent used is heated almost to its boiling point. For example, if dimethyl formamide is used as the solvent, the temperature may be 10 C. and the vacuum 50 Torr. The starting mixture is stirred further for to hours in vacuo and under cooling in order to insure a thorough equalization of the finished dispersion. Finally, the dispersion freed from air thus obtained is passed through a dissolving apparatus equipped with an agitator, in such a manner that the solution is gradually heated from about 60 to about 150 C., and preferably from about 80 to about 100 C. After filtering in the usual manner, the solution is spun immediately.

The particle size of the polymers may vary from about 10 to 100 and may preferably be in the neighborhood of 3011..

Monomers contemplated for copolymerization with acrylonitrilamay be acrylic acid amide, maleic acid amide, fumaric acid amide or their diamides; mcthacrylic acd methyl ester, styrene, vinyl chloride, viny-lidene chloride, vinyl acetate, vinyl carbazole, vinyl imidazole, vinyl pyridine etc.

The mixed polymers should contain at least percent of acrylonitrile so that the compound copolymerized therewith is present in an amount not exceeding 15 percent of the total.

In addition to dimethyl formamide, a variety of solvents can be used as follows: N-formyl pyridine, dimethyl sulfoxide, methane sulfonic acid methyl ester, glycolic acid nitrile, glutaric acid dinitrile, adipic acid dinitrile, valerolactone, n-methyl pyrrolidone, glycol carbonate.

In the drawing afiixed to this specification and forming part thereof, an installation for practicing the new process is illustrated diagrammatically by way of example.

In the drawing, the storage tank 1 is shown to contain the finely powdered polyacrylonitrile having a particle size below p. A vibrator 2 and a scattering device 3 provide for a continuous and uniform supply of the polymer to the kneader 5 which contains the solvent such as dimethyl formamide, for example. Through a valve 4 the kneader can be evacuated. The kneading device 6 effects an intensive working through and kneading of the dispersion formed in the kneader, whereupon the dispersion can be discharged into the storage vessel 7. In the dissolving vessel 3 the dispersion is heated up e. g. to about 100 C. Finally, the solution maintained at this temperature passes on, through a heated pressure pump 9, to the filtering device 10 which too can be heated and which is equipped with filtering candles. From the dosing pump 11 the solution which freed from air, is homogeneous and is heated to the required spinning temperature, is

passed on to the spinning nozzle.

The invention may be further illustrated by the following examples.

Example I In a vessel holding 20 liters, 2.4 kg. of finely ground polyacrylonitrile (K-value 89, particle size up to 100p) are added slowly, under thorough agitation, to 7.6 kg. of dimethyl formamide already contained in the vessel, at a temperature of 10 C. and a pressure of 20 Torr. The feed of the polyacrylonitrile most advantageously takes place by means of a built-in bucket wheel in a chronologically precisely dosed form, so that after every 5 seconds about 6 g. of polyacrylonitrile are added. On termination of the supply of polyacrylonitrile, the starting mixture is further stirred for another 8 hours at the same temperature in vacuo. The fine dispersion thus formed is now forced by means of nitrogen under a pressure of 5 to 10 at, into a cooled storage tank, to be passed on from here into a dissolving cylinder equipped with a built-in agitator. The dissolving cylinder is steam-heated to 100 C. It permits thorough dissolution of the dispersion; the finished solution is passed, at a temperature of about 100 C., through a filter press and from here to the dosing pump, whereupon the solution is spun, immediately, by the dry spinning method.

Example 11 22 kg. of polyacrylonitrile (K-value 89, particle size up to 100,u) are added from a storage container by means of a scattering device, to 78 kg. of dimethyl formamide, at a temperature of 15 C. and a pressure of 20-25 Torr. The solvent is placed in a kneader. By intensive kneading accompanied by evacuation which removes the air from the dispersion being formed, the dispersion is distributed after the lapse of 2-3 hours, by means of nitrogen under pressure, to two cooled storage containers. In

these storage vessels another evacuation takes place to remove any remnants of dissolved gases from the dispersion. The two storage vessels operate intermittently, i. e. while one passes the dispersion on to the dissolving vessel by means of nitrogen under pressure (e. g. 8 at.), the other is being evacuated. In the dissolving vessel the dispersion is heated e. g. to 100 C. to yield the homogeneous po'lyacrylonitrile solution free from air. This solution is maintained at the elevated temperature until it passes, finally, through a heated pressure pump to the likewise heated filter device and from there to the dosing pump which conveys the solution to the spinning nozzle.

The threads obtained from this solution, because of the protective character of the treatment, are extremely light and particularly uniform. They attain excellent mechanical strength. Thus for polyacrylonitrile, after the threads have been stretched to about ten times their original length, the strength amounts to about 4.4- g./den. (40-45 Rkm.).

Example III A copolymer consisting of 90 percent of acrylonitrile and 10 percent of acrylic acid amide, with a K-value of about 84, was treated as described in Example I, using glycolic acid nitrile as the solvent.

While We have disclosed the preferred embodiments of our invention and the preferred modes of carrying it into effect, it will be readily apparent to those skilled in the art that the invention as illustrated in the foregoing specification is susceptible to numerous variations without departing from the spirit of the invention or sacrificing of the advantages thereof. Accordingly, the scope of the in vention is to be understood as limited solely by the appended claims.

We claim: 1

1. The method of spinning solutions of polymers selected from the group consisting of polyacrylonitrile and copolymers thereof containing at least 85 percent by weight of combined acrylonitrile and another component selected from the group consisting of combined acrylic acid amide,

4 malelc acid amide, fumaric ac1d amide, acrylic acid d1- amide, maleic acid diamide, fumaric acid diamide, methacrylc acid methyl ester, styrene, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl carbazole, vinyl imidazole, vinyl pyridine, which comprises gradually dispersing the nitrile comminuted to a particle size ranging between about 10 and 100 at a temperature ranging between about 0 and 30 C. at the rate of about one gram per second in a cold solvent kept under vacuum, stirring the mixture 3 to 10 hours under continuous cooling, freeing the solution from air by gradually heating it to a temperature ranging from to 150 C. and then spinning by the continuous method.

2. The method of spinning solutions of polymers selected from the group consisting of polyacrylonitrile and copolymers thereof containing at least percent by weight of combined acrylonitrile, which comprises gradually dispersing the nitrile comminuted to a particle size ranging between about 10 and 1. at a temperature ranging between about 0 and 30 C. at the rate of about one gram per second in a cold solvent kept under vacuum, stirring the mixture 3 to 10 hours under continuous cooling, freeing the solution from air by gradually heating it to a temperature ranging from 60 to C. and then spinning after the continuous method.

3. The method of claim 1 in which the solvent is cooled down to a temperature ranging between 0 and 20 C.

4. The method of claim 1, in which the solvent is cooled down to a temperature ranging between 0 and 15 C.

5. The method of claim 1, in which a vacuum of at most 50 Torr. is maintained.

6. The method of claim 1, in which dimethylforrnamide is the solvent.

7. The method of claim 1, in which the rate of introduction of the polyacrylonitrile into the solvent is about 6 grams per 5 seconds.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF SPINNING SOLUTIONS OF POLYMERS SELECTED FROM THE GROUP CONSISTING OF POLYACRYLONITRILE AND COPOLYMERS THEREOF CONTAINING AT LEAST 85 PERCENT BY WEIGHT OF COMBINED ACRYLONITRILE AND ANOTHER COMPONENT SELECTED FROM THE GROUP CONSISTING OF COMBINED ACRYLIC ACID AMIDE MALEIC ACID AMIDE, FUMARIC ACID AMIDE, ACRYLIC ACID DIAMIDE, MALEIC ACID DIAMIDE, FUMARIC ACID AMIDE DIAMIDE, METHACRYLIC ACID METHYL ESTER, STYRENE, VINYL CHLORIDE, VINYLIDENE CHLORIDE, VINYL ACETAATE, VINYL CARBAZOLE, VINYL IMIDAZOLE VINYL PYRIDINE, WHICH COMPRISES GRADUALLY DISPERSING THE NITRAILE COMMINUTED TO A PARTICLE SIZE RANGING BETWEEN ABOUT 10 AND 100U AT A TEMPERATURE RANGING BETWEEN ABOUT 0* AND 30*C. AT THE RATE OF ABOUT ONE GRAM PER SECOND IN A COLD SOLVENT KEPT UNDER VACUUM, STIRRING THE MIXTURE 3 TO 10 HOURS UNDER CONTINUOUS COOLING, FREEING TURE RANGING FROM 60* TO 150*C. AND THEN SPINNING BY THE CONTINUOUS METHOD. 